Fuel cells refer to power generation systems that convert chemical energy of fuels into electric energy by electrochemically reacting fuel in cell stacks through combustion rather than the fuel being converted into heat. Fuel cells may be used for supplying power for industry, households and vehicles. In addition, fuel cells may be applied as power supplied for small electric/electronic devices, especially for portable devices.
Fuel cell systems measure temperature and control the temperature according to the measured temperature to improve system efficiency, to ensure the systems, and to improve durability of the fuel stacks in the long-term. For this, cooling performance is ensured by controlling RPMs of a cooling water pump and a cooling fan for stack cooling.
Herein, the cooling water pump and the cooling fan RPMs may be calculated by using a fixed RPM operational method based on temperature of a cooling water output from the fuel stack, or by using PI control methods that have a fixed gain value within a predetermined temperature range. Herein, fixed RPMs or fixed gains of PI control methods are determined by parameters that are initially tuned to the fuel cell system.
However, it is difficult for conventional methods using fixed RPMs that are initially tuned or methods applying fixed gains to respond phenomenon such as irreversible degradation or dry-out/flooding that occurs in the short term.
In addition, it is difficult for methods of applying fixed gains that are initially tuned to respond to changes in output demands that are changed in real time by a driver.
In addition, there is limit for RPM instruction values that are determined based on only temperature, which is the resultant phenomenon caused by changes in output demand of the driver, to active responses due to stack heat generation. In addition, feed-forward situations caused by heat and sudden temperature changes may frequently occur, and such situations may cause deterioration of system efficiency due to excessive RPM operation.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.